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ARROW-7341: [CI] Unbreak nightly Conda R job

One fix, one minor improvement, and also alphabetizing the env vars.

Closes #5985 from nealrichardson/unbreak-r-conda and squashes the following commits:

61c36b15b <Neal Richardson> Set UTF-8
a45fe3b12 <Neal Richardson> Unbreak nightly Conda R job

Authored-by: Neal Richardson <neal.p.richardson@gmail.com>
Signed-off-by: Neal Richardson <neal.p.richardson@gmail.com>